In recent years the market of the semiconductor industry has grown considerably for supplying integrated chips to companies which manufacture portable electronic devices. The integrated chips used to make these portable electronic devices, such as cell phones, PDAs, laptop computers and the like, are mostly made in emerging technology nodes. This is because emerging technology nodes offer higher density chips with greater performance and lower power consumption. These qualities are important to portable electronic devices which are continually striving to offer greater functionality while relying on relatively small energy sources (e.g., batteries). The demand for these products has driven the industry to devote many resources to developing low power integrated chips, often resulting in specific processes.
Memory is an important aspect of power consumption. Therefore, attempts to meet industry needs have also resulted in the emergence of new memory types and changes in existing memory types. For example, ferroelectric random access memory (FRAM), magnetoresistance random access memory (MRAM) and phase change memory (PRAM) are just a few of the many new memory types that are being increasingly researched as an alternative to present day industry standards. While each of these new technologies brings new advantages, they also bring new challenges. In particular, they require reliability to address new problems based upon non-traditional parameters.
Imprint is a reliability concern that has been observed in new memory types such as FRAM. Imprint is the tendency of a memory cell which remains in the same data state over a long period of time to retain a remnant of that data state upon being driven to another data state. For example, in FRAM memory imprint is the tendency of a ferroelectric capacitor which stays in the same polarization state over a long period of time to retain a remnant polarization upon being driven to another polarization state. Over time, imprint will create a growing offset voltage which eventually will make distinction between data states (e.g., “0” or “1”) impossible.